Brown algae contain a variety of sulfated polysaccharides. These sulfated polysaccharides are often generically called fucoidans or fucoidins. Their structures vary depending on the algae from which they derive. For example, sulfated polysaccharides extracted from algae of the order Fucales, Kjellmaniella crassifolia Miyabe, Laminaria japonica Areschoug, Cladosiphon okamuranus Tokida, Nemacystus decipiens (Suringar) Kuckuck and sporophyll of Undaria pinnatifida (Harvey) Suringar have structures different from each other. In general, a sulfated polysaccharide fraction prepared from one alga contains a mixture of several sulfated polysaccharide molecular species.
Sulfated polysaccharide molecular species of which the structures have been determined include sulfated fucans, sulfated fucoglucuronomannans, sulfated fucogalactans and sulfated glucuronofucans. Sulfated polysaccharides generally have some biological activities in many cases. For example, a sulfated fucan fraction has been reported to have a strong anticoagulant activity, and a sulfated fucoglucuronomannan fraction has been reported to have an apoptosis inducing activity against tumor cells. Therefore, attempts have been made in order to develop a pharmaceutical using a sulfated polysaccharide.
If one intends to develop a pharmaceutical using a sulfated polysaccharide, it is necessary to determine its structure. Use of an enzyme that degrades the sulfated polysaccharide is very advantageous for the determination of the structure. However, no enzyme that degrades a sulfated polysaccharide derived from a brown alga is commercially available. Furthermore, an enzyme that specifically degrades the sulfated polysaccharide is required in order to determine the structure of the sulfated polysaccharide. This is because sulfated polysaccharides derived from brown algae vary depending on the species of the algae.
A sulfated polysaccharide mixture derived from an alga of the order Fucales has been reported to have an anticoagulant activity, an activity of inhibiting colonization by a chlamydia onto uterine epidermal cells, an activity of suppressing an allergic reaction, an activity of suppressing grafted organ rejection and the like. Structures of fucoidans derived from algae of the order Fucales have been studied in order to elucidate the relationship between the activities and the structures. However, only average values for the structures have been proposed based on physicochemical analyses.
Several kinds of sulfated polysaccharide molecular species are present in a sulfated polysaccharide mixture fraction prepared from an alga of the order Fucales. Sulfated polysaccharides other than the molecular species that is responsible for the biological activity of interest are generally unnecessary. In some cases, such unnecessary molecular species may induce ill effects.
It would be very useful for elucidating the relationship between the biological activities and the structures if one could prepare oligosaccharides from a sulfated polysaccharide derived from an alga of the order Fucales with structural reproducibility. For example, an enzyme that degrades a sulfated fucoglucuronomannan contained in a sulfated polysaccharide mixture fraction derived from a brown alga to generate oligosaccharides is known (WO 96/34004). This enzyme acts well on a sulfated fucoglucuronomannan derived from a brown alga of the order Laminariales to generate sulfated fucoglucuronomannan oligosaccharides. However, it has almost no activity on a sulfated fucoglucuronomannan derived from a brown alga of the order Fucales.
For the reasons as described above, an enzyme that specifically degrades a molecular species contained in a sulfated polysaccharide mixture fraction derived from a brown alga of the order Fucales, a fucoidan fraction comprising more homogeneous molecular species, an oligosaccharide having an homogeneous structure produced by an enzymatic means, and methods for producing the same have been desired.